Condition controller



Jan. 7, 1941. FISHER EJ-AL 2,227,447

CONDITION CONTROLLER Filed Oct. 20. 1937 2"Sheets-Sheet l %Ymr6'n0/LQGeorge II. EishPr dharles B. flpangenberg W/ww M Jan. 7, 1941. a. H.FISHER ETAL comm'ron CONTROLLER Filed Oct. 20, 1937 2 Sheets-Sheet 2ciswmnik George HI Zsher I C harles' .B. ,6

pan enherg Patented Jail. 7, 1941 2,227,447

UNlTED STAT-ES. PATENT OFFICE CONDITION CONTROLLER George H. Fisher andCharles B. Spangenberg,

Minneapolis, Minn., assignors to Minneapolis- Honeywell 1 RegulatorCompany, Minneapolis, Minn., a corporation of Delaware ApplicationOctober 20, 1937, Serial No. 170,009 7 Claims. (Cl. 236-9) Thisinvention relates to a condition controller that in the normal or closedposition of the valve, and more particularly to improvements in the thespring biasing the valve open is held comcondition controllingarrangement disclosed in pressed. The result of more or less constantlythe co-pending application of Frederick S. Deniholding the springcompressed is that the spring son, Serial No. 150,575, filed June 26,1937. tends to weaken. Since this spring opposes the 5 In the abovereferred to application, there is action of the actuator responsive tothe secorid disclosed a condition controlling arrangement condition, anychange in the force exerted by this employing a valve positioned by aplurality of spring results in a change in the position of. theactuating devices each responsive to a different valve for a given valueof the second condition.

10 condition. Upon one of the conditions, such as In the third place,where the valve is used to 10 room temperature, assuming a predeterminedcontrol the flow of a heat producing medium, it valve is moved towardsopen position, this moveis always more adviseable to eliminate, as muchment being limited by an abutment which is as possible, any meanstending to bias the valve moved in accordance with the value of a secondopen. Each such biasing means increases the condition, such as boilerpressure. The valve possibility of the valve remaining open in the l5stem is provided with an extensible connection event of the failure ofcertain of the parts of the which is biased to its extended position butwhich apparatus.

is normally held contracted by an electromagnet An object of the presentinvention is to provide energized by a thermo-couple exposed to some adevice of the type previously discussed, in which Tl temperaturecondition, such as a pilot flame. In the disadvantages discussed areeliminated by the event that the pilot flame is extinguished for thesubstitution for the spring biasing the valve any reason, the biasingmeans associated with the open of a yieldable connection between theactuextensible coupling is efi'ective, by reason of the ator responsiveto the first condition and the deenergization of the magnet, to extendthe couvalve.

J pling and thereby move the valve to closed posi- The advantages of theimproved structure as tion. well as other objects of the invention willbe ap- While the device of the previous application parent from aconsideration of the accompanying possesses numerous advantages oversimilar prior specification, claims, and drawings of which: art devices,it has certain defects common to Figure 1 is an elevational view, partlyin secother similar prior are devices which renders its tion, of theimproved valve actuating mechanism; use less desirable. These defectsarise by reason Figure 2 is a schematic View of the temperature of thefact that" in order to permit the actuator control system employing theimproved controller responsive to the second condition to move the ofthepresent invention; valve towards closed position in spite of the factFigure 3 is a sectional view of a portion of the I73 that the value ofthe first condition is such as valve mechanism with the valve in openposition,

to call for the valve being open, the valve is and biased open by aspring and the actuator respon- Figure 4 is a sectional view of aportion of the sive to room temperature merely operates to move valvemechanism with the valve in closed position an abutment away from theend of the valve stem as the result of the extinguishment of the pilot4') to a position in which the spring is free to open flame. 40

the valve. The actuator responsive to the second Referring to thedrawings for a clearer undercondition thus needs tomerely oppose thisspring standing of the present invention, Figure 1 diswhen it move thevalve toward closed position. closes, as indicated above, the improvedvalve This spring results, however, in the necessity of operatingmechanism of the present invention.

a5 a biasing means in the extensible coupling which Referring to thisfigure, the valve body is genis sufllciently strong to overcome thespring biaserally designated by the reference numeral Ill. ing the valveopen. The result is that a rela- This valve body in comprises an inletconnection tively strong biasing means must be employed H and an outletconnection I2. Extending across in the extensible coupling, and in viewof the fact the interior of the valve body is the usual transf that theonly force opposing this biasing means verse partition I3 which isapertured to-provide is the relatively limited one exerted by the avalve seat l4. A valve disc l5 seats on the valve thermo-coupleenergized electro-magnet, considseat 14. The valve body I0 is closed atits upper erable difficulty is'experienced in avoiding faulty end by aclosure plate I! which is held in posioperation of the coupling. tion bya screw thimble nut 18. Secured to the 5-3 A second disadvantage of theprevious valve is closure plate 11 is a cup-shaped member I9 which 5 10,25 and 26 which are threadedly secured to the valve stem. The diaphragmactsas a seal-01f diaphragm to prevent gas from the valve casing frompassing into the housing 23.

The lower valve stem 2| is connected with 15 an upper valve stem 28. Thelower stem member 2| telescopes within the lower portion of the uppermember 28. The relative movement of these members is limited by a pin 26which is secured to the lower member 2| and which pro- I jects through aslot 30 in the upper member. It will be seen that the pin and slotarrangement forms an extensible connection between the two members sothat when pin 29 is in the lowermost-portion of the slot, the valve stemconstituted by members 2| and 28 is considerably extended. These twomembers are normally held against extension by an electromagnetarrangement generally indicated by the reference numeral 32, whicharrangement will be described in a subsequent paragraph.

As indicated previously, the valve disc i is positioned by thecooperative action of several actuating devices. The main actuator,which is normally controlled according to room temperature, comprises alever 33 which is pivoted at 3|. A spring 34 is associated with lever 33and serves to bias the same in a counter-clockwise direction. Secured tothe lever 33 opposite from the pivot point 3| is a hook 35 which fispivoted to lever 33 at 36. This hook 35 is adapted to be engaged by apin 31 secured to a gear 38. A spring 45 biases hook 35 to the rightagainst a fixed pin 46 so that hook 35 is held in the path of movementof pin 31. The gear 3' 38 is driven by a motor, not shown in Figure 1.On energization of the motor, the gear 38 is rotated in a clockwisedirection. The operation of the motor in the positioning of lever 33will be more apparent from a description of the 60. operation of theentire system as shown in Figure 2. Pivotally secured to the lever 33 bya pivot pin 39 is a cylinder 40. This cylinder has a collar 4| threadedinto the lower end thereof. The upper end of upper valve stem member 5528 is reduced as at 42, and this reduced portion extends through anaperture in collar member 4|. The upper end of the reduced portion 42 ofvalve stem member 28 is provided with a flange 43, and interposedbetween this flange and the collar 4| is a spring 44. The assemblageincluding cylinder 40 and spring 44 constitutes a strainreleaseconnection between lever 33 and the upper valve stem member 28. So longas the upper movement of valve stem member 28 is relatively unimpeded,this member will travel upwardly whenever lever 33 is rotated in aclockwise direction by the rotation of gear 38 in the same direction.The provision of spring 44, however, permits a change in the position ofvalve l5 even though lever 33 is 'in its extreme clockwise position, aswill be more apparent from the subsequent description.

A second actuating means comprises a bellows, only the housing of whichis shown in Figure 1,

and which is generally indicated by the reference numeral 48. Asindicated in Figure 2, the bellows 48 is connected through a capillarytube 49 to a bulb 58 containing a vaporizing fluid and placed in aliquid whose temperature controls the operation of the valve. Thebellows 48 serves to move valve stem member 28, and consequently thevalve disc l5, through a linkage mechanism, generally indicated by thereference numeral 52. This linkage mechanism may be of any type whichserves, upon continuous expansion of the bellows 48, to gradually movevalve i5 towards its seat until apredetennined minimum open position isreached, whereupon valve I5 is moved to its seat with a snap action. Thepreferred form of linkage mechanism and the one which is shown in thedrawing is that described in the co-pending application of Hugh Kelly,Serial No,41,097, filed September 18, 1935, which has matured intoPatent No. 2,116,605 of May 10, 1938. While the particular form of thelinkage mechanism forms no part of the present invention and accordinglyhas not been illustrated in its detail as in the aforementioned Kellyapplication, the operation of the same will be briefly described inorder to more clearly understand the operation of theactuating means ofthe present invention.

The linkage mechanism comprises three levers 54, 55 and 56, all of whichare pivoted upon a pivot pin 51. Secured to the bellows 48 is a member59 which bears directly against the lever 54 so that any'expansion ofbellows 48 causes movement of lever 54 in a clockwise direction. Alsobearing against lever 54 is a spring 68,-the tension of which may beadjusted by a suitable adjusting means 6|. It will be apparent that bysuitably adjusting spring 6 the efiect of bellows 48 on the position oflever 54 .can be correspondingly varied. The adjusting means 6| willordinarily be calibrated in degrees to indicate the setting of theapparatus. Lever 55 has a portion 63 which normally abuts against lever54 so that any clockwise movement of lever 54 imparts a similarclockwise movement to lever 55. Secured to the outer end of lever 55 isa flange 64. Extending between flange 64 and lever 56 is a spring 65which is guided by a pin 66, rigidly secured to the flange 64 andslidably extending through lever 56. Pin 66 is provided with a head 61engaging the lower surface of lever 56 to limit the movement of thislever away from lever 55. The spring 65 serves to form a strain releaseconnection between levers 55 and 56. So long as the movement of lever 56is not impeded by a force greater than that required to compress spring65, any clockwise movement of lever 55 causes a corresponding clockwisemovement of lever 56. As indicated most clearly in Figure 3, lever 56 isprovided at its lower edge with a turned-down car 68 which engages acollar 69 threadedly secured to the upper valve member 28. On movementof lever 56 in a clockwise direction, accordingly, the valve stemmembers 28 and 2| are moved downwardly causing valve I5 to move towardclosed position. The spring 65 is chosen so as to require a greaterforce to compress it than the spring 44 in the connection between lever33 and upper valve stem member 28. It will, accordingly, be seen that asthe temperature to which bulb 50 is subjected rises, causing anexpansion of bellows 48, levers 54, 55 and 56 are simultaneously movedin a clockwise direction causing valve l5 to be moved towards closedposition against the action of spring 44.

lid

iii!) bit till

Fill:

Cooperating with the lever members it and iii are two pivoted catchmembers it and it, as most clearly indicated in Figure 3. The catchmember it is biased by a spring 16 in a counterclockwise direction andis designed to engage lever lib after the same has been moved to aposition corresponding to the minimum open position of the valve. A pin73 is provided on the forwardly extending portion of lever b t tocooperate with catch "it and release the same at the proper pointagainst the action of spring it, as will be described later. The catchii is provided with a shoulder it against which the flange fit of leverit abuts in valve opening movement. A spring it biases catch it in aclockwise direction and the pin it of lever b t cooperates with a camshaped portion "iii of catch ill to release member t l against theaction of spring it, as will be more apparent from the subsequentdescription.

As previously indicated, the electromagnetic arrangement, generallyindicated by the reference numeral iii, serves to hold the lower valvestem member all and the upper stem member it in their retracted positionrelative to each other so that these two valve members act as a singleunit. This electromagnetic connection it comprises a core member illthreadedly secured to the upper valve stem lit and an armature memher itsecured to the upper nut member it and through this member secured tothe lower valve stem member ii. The core member "it is provided with awinding ill and surrounding the core it and winding ii is a casing til.The core member it is threadedly connected to the upper valve stemmember 28, as previously described, and serves to clamp the casing an inposition. A cup-shaped nut 8| serves to lock the core member it inposition. Located within this nut ti is a spring 82 which bears at itsupper end against the lowermost portion of the upper valve stem member23 and bears at its lower end against the nut member it which is securedto armature it and to valve stem ii. The spring iii is effective upondeenergization of the electromagnetic connection M to move armature "it!relative to core member it and to thereby move members ill and it totheir extended position in. which pin it is in the lower portion of slottit. In so extending the valve stem, valve it is moved to its closedposition regardless of the position of the upper valve stem member it.lit will, accordingly, be seen that the electromagnetic connection itconstitutes a safety connection to insure closure of the valve upondeenergization or the connection.

The energization of the electromagnetic connection is controlled by athermo-couple, generally indicated by the reference numeral iib. Thisthermocouple includes the usual elements tilt and till of differentthermo-electric characteristics. "While any two elements of suitablerelative thermo-elcctric characteristics can be employed, it has beenfound particularly desirable to employ an inner element of Constantan,an alloy comprising approximately 50% nickel and sea copper, and anouter member iii of stainless steel. This stainless steel employed maybe any suitable stainless steel capable oi adequately resisting the heatof the pilot burner flame. The two members it and til are joinedtogether at tit to provide the hot junction of the thermocouple. lFt isto be understood that where the thermo-couple is placed in a pilotflame, it is so placed that the junction bit is exposed to the pilotilame. The inner member M is connected to an insulated conductor it. Theouter member til is connected to a copper reducing sleeve ti, which inturn is connected to a copper tube it surrounding the insulatedconductor til. The inner conductor it is connected through a lead-interminal at to a conductor illi within the housing it, as best indicatedin Figure l. The copper tube it which functions as the other conductorconnected to the thermo-couple is connected through a second lead-interminal at to a conductor till, also located within the housing 23. Theconductors tit and ti are connected to opposite ends of theelectromagnet winding ill.

'The conductors til, at, iiii, ti and the winding ii are of relativelylarge cross section. The result is that very little resistance isoffered to the current generated by the relatively small electromotiveforce produced by thermo-couple tit. Accordingly, in spite of the verysmall electronictive force, a relatively large current flows throughwinding ll. Moreover, core member lid and armature member it arepreferably of Permalloy or some other material of very highpermeability. Consequently, the flux density in core member it andarmature it is sufficiently great, when the thermo-couple is energized,that when these two members are moved together by some external forcethe attraction between the two members is suficient to resist the actionof spring hi to separate them.

In Figure 2, the device of the present invention is shown embodied in atemperature control system. The various elements of the valve have beengiven the same reference characters as in the preceding description. Thevalve it is shown as controlling the flow of gas through a pipe itllleading to a gas burner iiill. Associated with the gas burner i it is apilot burner i III! which is connected through a pipe ll it to the mainsupply pipe Wt at a point behind the valve iii. Consequently, under allnormal conditions, the pilot burner i it is maintained ignited andserves in the conventional manner to i nite the main burner i it upongas being admitted thereto by the opening of valve iii.

The gas burner illlll forms the burner portion oi a hot water boiler,the boiler portion of which is brolren away at ti l to show the waterthere'- in. Pipes tit and lid lead from and to the boiler, respectively.Admission of secondary air to the burner is controlled by a secondaryair damper tit. This damper is pivoted at iii and is biased to an openposition. A. chain iii or other similar device extends over pulleys iiiland is connected to the lever of the valve mechanism. as previouslyindicated, the lever is rotated in a clockwise direction to open thevalve. Such cloclrwise rotation of lever serves to permit the secondaryair damper tilt to move to open position.

as previously indicated, the gear iiii is driven by an electric motor.This motor is indicated in Figure 2: by the reference numeral iilii. Themotor ilii comprises a rotor tit and a iicld winding iii. gear trainflit serves to connect rotor tilt with the gear iii. previouslyindicated, energization of the motor it'd causes cloclrwise rotation ofgear Connected to the gear lid is a shaft lit which drives a cam liiil,which in turn actuates a switch blade till. Switch blade iii is adaptedto be moved into engagement with contact idtl, this movement beingeffected.- by cam follower secured to switch blade iii'l, engaging araised portion I34 of the cam I30. The cam I30 is secured to shaft I29through a slip friction connection which causes, upon initial movementof shaft I29, an initial movement of cam I30 after which the cam merelyslides upon the shaft I29. The movement of the cam is limited by a pinI35 engaging the opposite ends of a recess I36 in the cam. The effect ofthis is that upon reverse rotation of shaft I29, cam I30 is immediatelyrotated in a reverse direction. The switch consisting of switch blade I3| and contact I32 operates to establish a maintaining circuit for themotor field winding I21, as will be more apparent from the subsequentdescription.

A thermostat I40 is provided to control the operation of motor I25. Thisthermostat is preferably located in a room or other space whosetemperature is to be controlled. The thermostat comprises a bimetallicelement I4I to which is secured a contact blade I42. Contact blade I42is adapted to engage with fixed contacts I43 and I44. Contact blade I42is so spaced relative to contacts I43 and I44 that upon movement ofcontact arm I42 to the left, it is first moved into engagement withcontact I43 and thereafter moved into engagement with contact I44.Bimetallic element I 4I is-so arranged that upon a temperature decrease,contact arm I42 is moved to the left and upon a temperature increase tothe right, as indicated by the legends C and H.

A step-down transformer I50 is used to supply low voltage power foroperation of the system. Transformer I50 comprises a line voltageprimary I 5| and a low voltage secondary I 52. The line voltage primaryI 5I is connected to line wires I53 and I54 leading to a suitable sourceof power (not shown).

One of the advantages of the type of device to which the presentinvention relates is the fact that it is possible to operate it safelyin the absence of electrical power. The valve may at any time be movedto open position providing the boiler temperature is sufliciently lowand the pilot is ignited by merely grasping lever 33 and turning it in aclockwise direction. A plunger I55 is provided for the purpose ofretaining the lever 33 in its valve open position when so moved. It willbe readily apparent that if lever 33 has been rotated in a clockwisedirection sufficiently, plunger I55 can be moved inwardly under-theleft-hand end of lever 33 and retained in this position. A

switch consisting of switch blades I56 and I51 is provided for thepurpose of insuring a return of the valve to automatic control uponpower restoration. The switch blade I51 is relatively fixed whereas theswitch blade I56 is moved to the right upon movement to the right ofplunger I55 by reason of the engagement of a push button portion I 59 ofplunger I55 with the blade I56. It will, accordingly, be seen that whenplunger I55 is moved to the right so as to retain lever 33 in its valveopen position, switch blades I56 and I51 are moved into electricalcontact.

Operation The various elements in Figure 2 are shown in the positionwhich they occupy when the pilot burner is ignited, the temperature towhich bulb 50 is responsive is relatively low, and the temperature towhich thermostat I40 is responsive is at or above the desired value. Letit be assumed now that the temperature to which thermostat I40 isresponsive decreases so as to cause first the engagement of switch bladeI42 with contact I43 and then with contact I 44. Engagement of blade I42with contact I43 has no eflfect whatsoever. As soon, however, as theblade engages contact I 44, the following circuit is established tomotor field winding I21: from the lefthand terminal of secondary I52through conductors I65 and I66, contact I43, contact blade I42, contactI44, conductors I61 and I68, motor field winding I21, and conductor I69to the other terminal of secondary I52. The establishment of thiscircuit causes field winding I21 to be energized with the result thatthe motor rotates in a direction to cause clockwise rotation of gear 38.After an initial movement of gear 38, cam I30 is effective to moveswitch blade I3I into engagement with contact I32. When this occurs, thefollowing maintaining circuit is established to field winding I 21: fromthe left-hand terminal of secondary I52 through conductors I 65 and I66,contact I43, switch blade I42, bimetallic element I4I, conductor I10,contact I32, switch blade I3I, conductors HI and I68, field winding I21,and conductor I69 to the other terminal of secondary I52. It will benoted that the new circuit is independent of contact I44 so that it isnecessary for the temperature to rise to a point wherein switch bladeI42 is separated from contact I43 before the motor is deenergized. Theresult of this is that an appreciable change in temperature is necessarybetween the starting and stopping of the motor. If it were not for thisdifferential, any slight chattering of the thermostat I40 would causerapid energization and deenergization of the motor I25.

Slightly after gear 38 has rotated suiiiciently to cause switch bladeI3I to be moved into engagement with contact I32 to establish themaintaining circuit previously traced, pin 31 is moved into engagementwith the hcok 35 so that hook 35 is moved upwardly rotating lever 33 ina clockwise direction. The result of this is. that the various elementsof the valve mechanism will move to the position shown in Figure 3wherein valve I5 is at its full open position admitting the maximumamount of gas to the burner IIO. The result of this is that thetemperature of the water in boiler II4 will begin to rise so as to causegradual expansion of bellows 48. The ecect of this, as previouslyexplained, is to cause a clockwise movement of levers 54, 55 and 56,which in turn causes movement of valve I5 towards closed position. Thismovement of valve I5 is permitted by reason of the yieldable connectionincluding spring 44 and cylinder 40.

Under normal conditions, valve I5 will be moved to a position relativeto its seat to maintain substantially just the right amount of gas flowso that upon substantially continuous operation of the burner, the roomtemperature ismaintained at the desired value. If, however, thetemperature of the water becomes sufiiciently high to cause valve I5 tobe moved to a position requiring too small a flow to properly sustaincombustion, the valve is abruptly moved to full closed position untileither the water tempertaure or the room temperature is reduced.Referring to Figure 3, it will be noted that the upper leg of catchmember 10 lies in the path of movement of lever 56. The apparatus is sodesigned that when the valve I5 reaches a desired minimum open position,further movement of lever 56 is prevented by catch 10. In view, however,of the strain release spring 65, further movement of levers 54 and 55 ispossible.. The result of such movement is that pin 13 aaavnav is moveddown towards the horizontal a oi the pivoted catch it. As soon as thismovement has continued sumcicntly tar, the pin it is ei iective to rockthe catch in a clockwise direction against the action of spring it,moving the upwardly extending leg thereoi out irom underneath the leverht. as soon as this tattoo place, lever at is free to move downwardlyand spring or by reason of the compression under which it has beenplaced is eilective to cause such movement with a very abrupt action.Thus valve disc it is caused, during the initial expansion of bellowsit, to assume a position cor responding to the temperature to which bulbto is subjected. As soon, however, as a minimum flow position isreached, further movement oil the valve it is temporarily terminated,and as soon as the temperature to whichbulb at is subjected has risensuihciently the valve is moved with a snap action. to its seat. Theeffect or" this is that the valve is gradually throttled during theinitial portion of its movement and is moved with a snap action duringthe final portion of its movement. in this manner, any danger oi apop-back in the gas mixer, by reason of too small a gas flow to theburner, is avoided.

The moving of valve disc it to its closed position will terminate theoperation oi burner tit and will eventually cause a reduction in thewater temperature to which bulb ht is subjected. This will causecounter-clockwise movement oi. lever ht. Upward movement oi the valve tois prevented, however, by reason or the fact that upon valve it beingmoved to its closed position the flange 64 of lever 55 was moved underthe shoulder 74 of catch member "ll. Accordingly, valve It remains inits closed position until the temperature to which bulb to is subjectedhas dropped to a point where lever W is moved in a. counter-clockwisedirection sumciently to cause engagement of the pin "it with theinclined surface 15 of catch member "it. When this occurs, pin it iseffective to rotate the catch member it in a counter-clockwise directionagainst the action oi its biasing spring it to cause the latchingsurface "it to be moved out of engagement with lever When this occurs,the spring it in the connection between lever and the upper valve memberth is eiiective to cause valve lit to be moved ab ruptly until shoulderoi lever again abuts lever tit. Thereafter the position oi valve willdetermined by the position oi lever as determined by the temperature towhich bulb tilt is subjected.

Whenever the space temperature or other temperature to which thermostatt lt is responsive rises to a high enough value to come separa tion oicontact blade hill irorn contact the circuit to field winding til isinterrupted. The biasing spring is thereupon eflective to ro tate gearthe gear train tilt), and the motor in a direction opposite to that inwhich they moved upon energiaation oi" the motor.

' The result is that valve is moved to closed position regardless oi theboiler water temperature.

it when the valve is in its open position, shown in Figure 3, the burnerpilot tit is ezrtin guished for any reason whatsoever, the tempe atureto which the hot junction oi thermo couple th is subjected willimmediately decrease so that thermo-couple tit no longer suppliessuihcient energy to the electromagnetic conneo tion hi to resist theaction oi spring tit.

then change the adjustment of thermostat t lt momentarily so that itceases to call for heat, deenergizing motor tlt causing the upper valvestem member it to be moved downwardly into valve closed position whereinthe core member it is in engagement with the armature member "it. inview of the fact that the pilot burner ttt has been re-ignited so as toreenerglze the winding oi the core it, the electromagnetic connection isagain efiective and as soon as there is a call for heat the valve stemmembers it and it will again move together as a unit.

as previously indicated'this type or device is particularly adapted foroperation in the event of power iailure. all that it is necessary to dounder these circumstances is to grasp the righthand end oi lever itrotating it in a clockwise direction to a substantial valve openposition wherein plunger that may be moved under the left-hand end orlever lit to hold the valve in such substantial open position. With theelements in this position, the valve is no longer under control oithermostat lit. The operation, however, is entirely sate inasmuch as theactuator comprising bellows it and bulb Was well as the pilot responsiveactuator is still efiiective. Thus, under these circumstances as theboiler water temperature rises, the valve is moved towards closedposition in the manner previously described, thus preventing anexcessive boiler temperature. at the same time, it at any time the pilotburner ttt is extinguished the valve is abruptly moved to closedposition and ca again be reopened until the pilot burner lit inre-ignited. The moving oi plunger tilt to the right causes switch bladetliti to be moved into contact engagement with switch blade tall, asnoted previously. The engagement oi these two contacts has no etlect solong as the power is oil. its soon, however, as power is restored, anenergiaing circuit is established to ileld winding ttl't as iollows:irom the leithand till terminal oi secondary that through conductors andtltti, switch blade.t'li't, switch blade tittt, conductors tilt andtilt, i-leld winding ill, and conductor to the other terminal oisecondary it will he noted that the establishment at this circuit isentirely independent oi thermostat t ttt so that ileld winding tit willbe immediately energized upon restoration oi power. The plung er tilt isso located that it does not hold valve in its completely open position.accordingly, scenes the iield winding tilt is energized in the mannerjust captained, lever and valve it are moved slightly iurther, movinglever out oi engagement with plunger the. i v soon this occurs, the biasupon blade is reflective to retract the same to the leit, at the sometime moving plunger tot teach to the po sition shown in the drawingwherein is out oi the path oi movement oi leve This re sults in motoragain being placed under com trot oi thermostat t ltt.

it will he noted that by reason oi the elimina tion oi any springbiasing valve it open, spring till t lt

8| inserted between the two elements of the electromagnetic connection32 need be capable of exerting only a relatively small force. At thesame time by elimination of the spring biasing the valve open, the onlyspring that is under tension when the valve is in its closed position isthe spring 8|. Thus, the only spring Which can possibly be weakened as aresult of the fact that it is maintained in a permanent stressedcondition is spring 8|. However, by reason of the fact that this springsonly function is to separate the members against what little residualmagnetism may remain and hold the valve firmly on its seat, it can beconsiderably weakened without in any way interfering with the operationof the system. The spring whose tensional strength affects the values atwhichthe apparatus is operated is the spring 44 which by reason of itslocation is an element of a strain release connection between lever 33and the valve stem is under no stress whatsoever when the valve isclosed. -It will be readily apparent that the improved device of thispresent application overcomes the disadvantages pointegl out in thedevice described and claimed in the co-pending Denison application. Itwill further be seen that these disadvantages have been overcome withoutcomplicating the arrangement in any respect whatsoever.

While we have shown a specific embodiment of our invention, it is to beunderstood that this is for purposes of illustration and that ourinvention is limited only by the scope of theappended claims. I

We claim as our invention:

1. In combination, a unitary condition controlling element movablebetween first and second positions, a two position motor means,yieldable connecting means between said motor means and said element,means controlling said motor means in accordance with the value of afirst condition and operative upon said condition assuming apredetermined value to cause said motor means to move to a positioncorresponding to the second position of said element and hence yieldablyto move said element towards said second position, and means including adevice responsive to a second condition and operative gradually to movesaid element against the action of said yielding connection back towardssaid first position as said second condition changes in a predetermineddirection, said yieldable connecting means being in a state ofrelaxation whenever the position of said element is determined solely bysaid motor means.

2. In combination, a unitary condition controlling element movablebetween first and Second positions, a two position motor means,yieldable connecting means between aid motor means and said element,means contrzlling said motor means in accordance with the value of afirst condition and operative upon said condition assuming apredetermined value to cause said motor means to move to a positioncorresponding to the second position of said element and hence yieldablyto move said element towards said second position, and means includingmeans responsive to a second condition the value of which is normallyincreased as a result of said condition controlling element being movedtoward said second position, said means being operative upon the "valueof said'condition increasing to move gradually said element against theaction of said yielding connection back towards said first position,.said yieldable connecting means being in a state of relaxation wheneverthe position of said element is determined solely by said motor means.

3. In combination, a condition controlling element movable between firstand second positions, a two position motor means, yieldable connectingmeans between said motor means and said element, means controlling saidmotor means in accordance With the value of a first condition andoperative upon said condition assuming a predetermined value to causesaid motor means to move to a position corresponding to the secondposition of the element and hence yieldably to move said element towardssaid second position, means including a device responsive to a secondcondition and operative gradually to move said element against theaction of said yielding connection back towards said first position assaid second condition changes in a predetermined direction, anextensible connection between said yieldable connecting means and saidelement, yieldable means tending to extend said connection to move saidelement to said first position, and condition responsive meansrestraining said yieldable means.

4. In combination, a main burner, a pilot burner, a valve controllingthe flow of fuel to said main burner and movable between maximum andminimum flow positions, a motor means, yieldable connecting meansbetween said motor means and said valve, means controlling said motormeans in accordance with a first condition indicative of the demand forburner operation and operative upon said condition assuming apredetermined value to cause said motor means yieldably to move saidvalve towards said maximum flow position, means responsive to a secondcondition indicative of the demand for burner operation to move saidvalve against the action of said yieldable connection back towards saidminimum flow position as said second condition changes in apredetermined direction, an extensible connection between said yieldableconnecting means and said valve, yieldable means tending to extend saidconnection and move said valve to closed position, and means responsiveto the temperature adjacent said pilot burner operative to restrain saidyieldable means when said pilot burner is ignited.

5. In combination, a main burner, a pilot burner, a valve controllingthe flow of fuel to said main burner and movable between maximum andminimum flow positions, a motor means, yieldable connecting meansbetween said motor means and said valve, means controlling said motormeans in accordance with a first condition indicative of the demand forburner operation and operative upon said condition assuming apredetermined value to cause said motor means yieldably to move saidvalve towards said maximum flow position, means responsive to a secondcondition indicative of the demand for burner operation to move saidvalve against the action of said yieldable connection back towards saidminimum flow position as said second condition changes in apredetermined direction, an extensible connection between said yieldableconnecting means and said valve, yieldable means tending to extend saidconnection and move said valve to closed position, and means includingan electromagnet and a thermo-couple exposed to the pilot flame andadapted to energize said electromagnet, said last named means beingoperative to restrain said yieldable means when said pilot burner isignited.

6. In combination, a valve movable between minim and maximum flowpositions, a valve stem connected to said valve, a motor, connectingmeans between said motor and said valve stem including a connectionyieldable only in the direction oi the minimum flow position, meansincludinn a device responsive to a first condition for conti'ciiing theenergization of said motor and cdcctivc upon said first conditionassuming a predctcred value yieldably to move said valve towards saidmaximum flow position, an extenciiolc connection in said valve stem,yieldable means tending to extend said connection to move said valve tominimum flow position, means recnonsivc to a second condition operativeto resti' said yieldabie means so long as said second condition exists,and means including a device rcspoive to a third condition and operativeon sic connected to said valve, a motor, connecting means between saidmotor and said valve stem including a connection yieldable only in thedirection of the minimum flow position, means including a devicevresponsive to a first condition for controlling the energization ofsaid motor and effective upon said first condition assuming apredetermined value yieldably to move said valve towards said maximumflow position, an exten-- sible connection in said valve stem, yieldablemeans tending to extend said connection to move said valve to minimumflow position, an electromagnet operative when energized to restrainsaid yieldable means, a thermo-couple responsive to a temperaturecondition and operative normally to maintain said electromagnetenergized, and means including a device responsive to a third conditionand operative on said valve stem at a point between said extensible andsaid yieldable connection to move said valve towards said minimum flowposition as said third condition changes in a predetermined direction.

